A CDMA 1X/EVDO hybrid access terminal (mobile device) is a hybrid system that has evolved from the CDMA 2000 system. EVDO stands for Evolution Data Only or Data Optimized and, as suggested by this, is a data only system. EVDO is also alternatively known as High Rate Packet Data (HRPD). One advantage of EVDO systems is that they allow a higher transfer rate for data. They are also useful to carriers to clear the 1X system voice capacity by removing data traffic from the 1X system.
Once a hybrid access terminal has an EVDO session established, applications that use the EVDO air interface will need to open a point-to-point protocol (PPP) session using Simple IP or Mobile IP. Current systems have two options for tying the PPP session with the EVDO session. By default, the two are never tied. Alternatively, the two may be always tied together.
The problem with this is that if EVDO and PPP sessions are always tied together, situations exist where the EVDO session does not necessarily need to be closed when the PPP session is closed, or the PPP session does not necessarily need to be closed when the EVDO session is closed. If the two are not tied together, there are situations where it is desirable to close both the EVDO session and the PPP session together and this may not happen if the two are not tied together.